1. Field of the Invention
The present invention relates to a high-reflectance silver mirror employing a phosphorus-containing glass base material and a process for production thereof. The present invention relates also to a reflecting optical element employing the silver mirror.
2. Related Background Art
Conventionally, the reflection layer of a mirror or the like on the reflection face thereof has been formed of a thin film of a metal with a high reflectivity such as aluminum and silver. In particular, silver has widely been used owing to its prominently high reflectivity in the visible wavelength region.
The thin metal layer of aluminum, silver, or the like has conventionally been formed by a dry process such as vacuum vapor deposition, sputtering, and ion plating. In particular, as for the silver film, it can also be formed by a wet film-forming process exemplified by a silver mirror reaction.
The thin metal film used in the silver mirror may be constituted of a single metal layer, or may have a laminate structure in combination with another layer such as an oxidation-preventing layer for preventing oxidation of the metal thin film or a reflection-increasing film for improving the reflection properties of the thin metal film.
In recent years, optical elements in various forms are commercialized which are produced by melting low-melting glass and forming the resulting melt in a mold into a desired shape of optical elements. The low-melting glass contains phosphorus in many cases.
However, the high-reflectance silver mirrors of the prior art involve disadvantages given below.
The conventional reflecting silver film used in the silver mirrors is usually formed by means of a dry vacuum deposition process such as vacuum vapor deposition, sputtering, and ion-plating. By such a dry process, the reflecting silver film may be formed with difficulty on an article in a complicated shape, or the production thereof on the complicated article may require a complicate film-forming apparatus and a complicate production process, raising the film forming cost.
For the cost reduction of the film formation, wet processes are investigated: the process including the silver mirror reaction, and an autocatalytic electroless plating. However, the phosphorus-containing glass as the base material is less resistant to chemicals. Therefore, in formation of the film by a wet process directly on the phosphorus-containing glass base material, the phosphorus component may be dissolved out so that the base material may be collapsed, and in other words, the surface of the base material may be damaged remarkably to become useless for optical elements, disadvantageously.
An object of the present invention is to provide a silver mirror producible at a lower cost and having a high-reflectivity. Another object of the present invention is to provide a process for producing the silver mirror. A still another object of the present invention is to provide a reflecting optical element employing the silver mirror.
The present invention provides a high-reflectance silver mirror comprising a base material made of phosphorus-containing glass and a high-reflectance film comprising a silver layer formed thereon, the high-reflectance film being formed by a wet film-forming method on an acid-resistant protection film provided on the base material.
The present invention also provides a reflecting optical element having a light travel path and a light reflection face provided in the light travel path, the light reflection face comprising the high-reflectance silver mirror of the above constitution.
The present invention also provides a process for producing a high-reflectance silver mirror comprising a base material made of phosphorus-containing glass and a high-reflectance film comprising a silver layer formed thereon, comprising the steps of coating the base material with an acid-resistant protection film, and forming the high-reflectance film on the acid-resistance protection film by a wet film-forming method.
According to the present invention, the base material made of phosphorus-containing glass is protected by a protection film formed of an acid-resistant material, whereby the silver layer can be formed by a wet film-forming process without causing the phosphorus-containing glass to be dissolved in the solution and also without causing the base material of phosphorus-containing glass to be collapsed.